Evaluation on the Potential Use of Natural Subbase Dust as Alternative Filler Material for Hot Mix Asphalt Design, Jimma Town

Abstract

A well-designed asphalt mixture is expected to serve effectively for many years under a variety of loading and environmental conditions. Bituminous concrete is one of the highest and costliest types of flexible pavement. One of the main problems in the construction of asphalt paving mixture is obtaining sufficient amount of filler material and high cost of the use of OPC, HL or marble dust as filler material. HL and OPC are active fillers which has high adhesion properties as the result Asphalt Institution restricted the use of only a maximum limit of 2%. Whereas inert fillers like marble dust and stone dust can be used with a proportion of up to 8% to improve the aggregate grading requirements. But these materials has a problem of issues like abundance, accessibility, high grinding effort cost, high transportation cost. To alleviate this problem it is important to come across alternative filler material that can address this gap. The study has investigated the potential use of natural subbase dust (NSD) as alternative filler material and their characteristic on the effect of hot asphalt mixture was identified. This research was conducted by using Experimental Research Design. In total, 48 samples were prepared according to ASTM D1559, of which 30 of them have been used to determine the OBC and the rest to find out the effects of adding different percentages of NSD to the asphalt mixture and for the control mixtures. For this purpose, five different bitumen contents were used (4%−6% with 0.5% increments). Aggregate mixtures blended without filler and with NSD filler were investigated to evaluate their Marshall properties on HMA mixtures. Four varying percentages of NSD ranging from (2% - 8% at 2% increments) was used for Marshall experiments. And for control mix 2% Hydrated Lime (HL) and 2% Ordinary Portland Cement (OPC) were used in the mixture besides, 4% Marble Dust was used as reference. The aggregates were blended by using Job mix formula to obtain the percentage of material proportion. As the result for aggregates blended without filler G-1(26%), G-2(23%) and G3(51%) proportion was used where as for aggregates blended with NSD filler, G-1 (26%), G-2 (22%), G-3 (46%) and G-4 (6%) was utilized. Where G-1 is Coarse Aggregate 3/4, G-2 is Intermediate Aggregate 3/8, G-3 is Fine Aggregate and G-4 is NSD filler. Based on Marshall test results the OBC was found 5.1% by the total asphalt mix. Furthermore, examining Marshall mixes containing different percentages of filler showed the optimum percentage of NSD was 6% by the total mix weight. All the Marshall properties of stability, flow, VFB, VMA & air voids parameters at 6% NSD filler by the total weight were consistent with in the range of the standard specifications. The investigation of NSD filler has resulted good effects by improving the aggregate grading and filling the voids on the asphalt mixture. Furthermore, the outcome of Marshall parameters like stability, air voids and bulk density values were consistent with the standard specifications. Therefore, NSD filler can potentially be used an alternative filler material in HMA with optimum filler content of 6% by total weight of any surface aggregate mixtures. Besides, it is recommended to exercise the use of NSD as filler material in HMA projects in order to ensure the quality of works, save transportation cost and save time spend to import other filler materials from far away. It is also recommended combining NSD filler with other materials may produce better outcome on the effects on the asphalt mix properties.